This invention relates to systems and methods for reconstructing acoustic and/or electromagnetic properties of objects with diffraction tomographic procedures using filtered backpropagation techniques wherein the sources of acoustic and/or electromagnetic energy may be located on any arbitrary surface totally or partially surrounding the object, and the detectors of such energy likewise may be located on any arbitrary surface totally or partially surrounding the object.
For purposes of this application and the claims herein, it should be understood that the waves of energy which propagate and diffract according to the invention include but are not limited to sonic or electromagnetic waves. The term "sonic wave" shall be interpreted as broadly as possible and shall be understood to include all elastic wave phenomena in liquid and solid materials including, but not limited to, acoustic, compressional, shear, and elastic waves. The term "acoustic wave" shall be interpreted herein to be the equivalent of "sonic wave". The term "electromagnetic wave" shall be interpreted in its broadest sense and shall include, but not be limited to infrared rays, X-rays, and the class known as "optics".
Further, for purposes of this application, the term "arbitrary surface" shall be understood in its broad sense and shall include all surfaces as well as the term "boundary".
More particularly, this invention relates to diffraction tomographic procedures using filtered backpropagation techniques where the plane wave or fan beam (cylindrical or spherical wave) sources and the detectors are located on arbitrary surfaces, and the object of reconstruction may be either a two or three dimensional body.
In the special cases where the detector surface used in the invention is as infinite plane on one side of the object, the methods reduce to the fixed detector plane invention disclosed in copending Ser. No. 533,391. If the single detector plane is allowed to rotate so as to remain perpendicular to the source of energy, the method reduces to the classical ultrasound diffraction tomographic technique described in copending Ser. No. 441,323.
As disclosed in Ser. No. 441,323, computer-aided diffraction tomography which attempts to account for the diffraction of acoustic energy as it propagates through a body of interest has been known in the art. While the proposed solutions prior to Ser. No. 441,323 were inadequate as regards reconstruction accuracy or practicality, the backpropagation filter and filtered backpropagation technique disclosed in Ser. No. 441,323, permitted the tomographic reconstruction of an investigated object with a practical accurate system and method which properly accounted for the diffraction of acoustic and/or electromagnetic waves propagating through an object. The detailed disclosure in Ser. No. 441,323 described ultrasound embodiments with coplanar sources and detectors which simultaneously rotated around the object, and provided the basis for the use of backpropagation filters and filtered backpropagation techniques in the diffraction tomography arts. The Background section of Ser. No. 441,323 also provided some of the theoretical foundations of filtered backpropagation.
Copending Ser. No. 533,391 expanded upon Ser. No. 441,323 to provide optimal reconstructions where the detector array was fixed in space such that the sources and detectors were non-coplanar, and discussed slant stack procedures for generating insonifying plane waves having various angles of insonfication from a fixed cylindrical wave source array. Also, among other things, Ser. No. 533,391 provided a method for the direct three-dimensinal reconstruction of an object.
While Ser. Nos. 441,323 and 533,391 provided the groundwork for making the field of ultrasound diffraction tomography viable, the systems and methods discussed therein described particular geometries. Others working with filtered backpropagation in the acoustic tomography arts such as M. F. Adams and A. P. Anderson; "Synthetic Aperture Tomographic Imaging for Microwave Diagnostics", IEE: (England, April, 1982), have disclosed nothing more than the simplest geometry of Ser. No. 441,323 which is not always practicable or desirable.